BAD DOG, The other thing I didn't mention is that I also had to go with short stacks in order to get through my 10' garage door. When I built the garage 5 years ago, I had only the B61 and B815 (with 864 V8), and 10' was a convenient height. But now the Superliner needs to live in there during the winters, so I went with short stacks - which means that the outlets are only about a foot and a half above the top of the cab windows. I have the same single 5" pipe running under the cab, then I went through a Y and ran horizontally out to the sides and through 90 elbows to vertical all in 5", then got stacks that start at 5 but expand to 6. They're only 5' long, so maybe the combination of short length, expansion in the stack itself, and low outlet height makes a difference. What was your 866 in, and how did you mount and plumb those pipes? I'm thinking of putting duals on the B815 someday. There was a guy at the Auburn, Indiana ATHS show back on 2005 who had a nice setup on his B815, but I didn't pay enough attention to how he had mounted the non-standard stack on the driver's side. My first step will be to put on the single 4" straight pipe that came off my B61 when I switched it to duals back on '05, but I don't think I'll be satisfied with that forever.